Components used in high stress, high temperature applications ("high intensity" components) typically are provided with protective coatings to prevent material oxidation and hot corrosion during service. One type of protective coating for high intensity components, such as gas turbines, is an overlay coating. A popular overlay coating has a chemical composition of "MCrAlY"--where "M" is nickel, cobalt, or both, Cr is chromium, Al is aluminum, and Y is yttrium.
Certain types of components are subject to particularly high stress and high temperature conditions during use (hereinafter called "super high intensity" components). Examples of super high intensity components are jet engine parts and turbo-superchargers. In order to withstand the extreme service conditions, super high intensity components typically are made of a base material known as a "superalloy." Superalloys exhibit high temperature mechanical integrity with an unusual degree of oxidation and creep resistance. Popular protective coatings for super high intensity superalloy components are thermal barrier coatings (TBCs). TBCs maintain the temperature of the superalloy substrate at an acceptable operating level during service.
The temperatures at which components are expected to operate continue to increase. New coatings are needed which will protect high intensity and super high intensity components at ever higher temperatures.
Certain metal carbides and metal borides have extremely high melting temperatures. For example, hafnium carbide has a melting temperature of 3890.degree. C. and tantalum carbide has a melting temperature of 3880.degree. C. Metal carbides also exhibit desirable brittle to ductile transition temperatures in the range of 1725-1980.degree. C.
A high temperature coating made of a refractory metal carbide and/or metal boride and comprising between about 20-30% particulate silicon carbide theoretically should provide excellent high temperature stability. In fact, the United States Air Force recently initiated a new program--Integrated High Pay-Off Rocket Propulsion Technology (IHPRPT)--to incorporate such advanced materials into rocket and space propulsion systems. Methods are needed for preparing high temperature coatings comprising refractory metal carbides and/or refractory metal borides.